Conventionally, a lighting device (lighting circuit) is used for controlling lighting of a light source. For example, in a light fixture, such as a headlight, in vehicles such as automobiles, a high intensity discharge (HID) lamp is provided as a light source, and a lighting device (ballast) is provided for controlling the lighting of the HID lamp.
As lighting devices are being miniaturized and made thinner, electronic components mounted onto circuit boards (printed boards) of lighting devices are also progressively being miniaturized and made thinner in recent years. For example, with regard to transformers which are one of the electronic components of lighting devices, there is a trend towards replacing transformers configured by winding copper wires around a bobbin with thin sheet transformers.
Sheet transformers include, for example, winding patterns such as a primary coil and a secondary coil formed on plural layers of a circuit board, and a core attached to the circuit board (see Unexamined Japanese Patent Application Publication No. 2010-178439).